The present invention is related to a process for producing inorganic porous materials in a capillary (or more generally in a confined space as defined below) and materials prepared by such process. These materials are favorably applied to producing capillary columns for electrochromatography, porous catalysts, or enzyme supports. Such inorganic porous columns can be favorably applied to liquid, gel-permeation and gas chromatography. These columns can be used unmodified or modified e.g. by covering their surface with molecules like hydrophobic hydrocarbon ligands (e.g. octadecyl ligands) or like hydrophilic ligands like 2,3-dihydroxypropyl derivatives. The ligands of such modified columns can be further modified using known procedures. Porous catalysts or enzyme supports can be prepared by adding enzymes, e.g. glucose isomerase, or catalytic metal elements, e.g. platinum and palladium.
The sol-gel method is one of liquid phase reaction paths to produce inorganic porous materials, especially silica gels. The sol-gel method denotes widespread processes in which polymerizable low molecular weight species are first generated, and through polymerization reactions, aggregated or polymerized materials are finally obtained. For example, the sol-gel method can be applied by hydrolyzing metal alkoxides, metal chlorides, metal salts or coordinated compounds which typically contain carboxyl or beta-diketone ligands. A process of this kind is disclosed in EP 0 363 697. In this process an organic polymer is used, which is compatible with the solution of the metal alkoxide or its polymer, and which undergoes phase separation during the hydrolysis-polymerization step. The materials produced by this process display connected open pores with a narrow range of the pore size distribution. Improvements to the process as disclosed in EP 0 363 697 are subject matter of WO 95/03 256 and WO 98/29 350. WO 95/03 256 disclose the use of special pore forming agents, whereas WO 98/29 350 disclose the use of precursors of such pore forming agents. All three documents disclose procedures useful to produce monolithic porous bodies. Common to the procedures disclosed in these three documents is that the porous formed body produced is taken out of the cast used for forming it. Such a procedure is not amenable if the porous formed body has a small dimension in at least one direction, because such thin structures would easily be teared or break. On the other hand the procedures disclosed in these three documents do not yield porous bodies which are fit liquid tight to their cast, because the inorganic material shrinks considerably during processing.
The existing capillary columns for electrochromatography is produced by packing inorganic materials such as silica gel beads into a capillary by physical means. It is necessary for the column packing materials used in the electrochromatography to carry electrostatic charge on their surfaces. Accordingly, inorganic porous materials which retain stable negative charges in a neutral pH condition, especially silica gels, are widely used.
Particle-packed capillary columns for electrochromatography have been prepared by physically packing inorganic particulate materials into a capillary. In order to avoid the change in the packing state of the particles due to their motion in the capillary, the both ends of a capillary are fitted with the parts called xe2x80x9cfritxe2x80x9d with relatively low porosity.
Particle-packed capillary columns are disadvantageous in the points that: (a) the packing procedure is complicated and time-consuming. (b) the reproducibility of the packing state, and correspondingly that of an excellent analytical performance, is poor. (c) Since the homogeneous packing of an entire capillary becomes increasingly difficult as the column length increases, an improvement of the analytical performance by increasing the total column length is not practical.
In addition, particle-packed capillary columns equipped with the frits at both ends frequently causes bubbling at the space between the frit and packed-beds, thus requires additional pressurization to the normal chromatographic operation.
In spite of the fact that the analytical performance of a capillary column is governed by its inner porous structure directly related to the packing state of the particles, there has been no established particle-packing method which produces the stable and reproducible packing state.